1. Related Application
This is related to a patent entitled "Low Wind Load Parabolic Antenna", Ser. No. 07/732,651 filed Jul. 19, 1991, filed concurrently with this application.
2. Field of the Invention
The present invention is related to the field of microstrip antennas and feeds and, in particular, to a stacked dual dipole feed for a multichannel multipoint distribution service (MMDS) parabolic antenna.
3. Statement of the Problem
Significant goals of the MMDS industry are to provide rooftop antennas having (1) the lowest possible manufacturing costs with consistently uniform performance, (2) high gain, (3) high directivity, and (4) high levels of rejection for cross-polarized signals. An example of a prior MMDS antenna is the Conifer Model PT-1000 which is disclosed in U.S. Pat. No. 4,295,143, commonly owned by the assignee of the present invention.
A need exists for an MMDS antenna having a sharper more directive feed and antenna patterns for improved rejection of unwanted signals. A need further exists for obtaining higher gain from a given size main reflector and having an improved voltage standing wave ratio (VSWR) over the full bandwidth. A need further exists to improve the balance to unbalance transition from the feed to coaxial cable connection.
Finally, a need exists to use fewer parts to assemble the feed so as to reduce labor costs. Present manufacturing processes rely on human skill in the assembly of the feed components. Hence, human error enters the assembly process and quality control must be used to ferret out and minimize such human error. This adds to the cost of the feed. Such human assembled feeds are also inconsistent in performance.
4. Solution to the Problem
The stacked dual dipole feed of the present invention is of one piece construction and does not utilize any external components. This eliminates the human error factors found in prior art feeds and provides a manufactured feed of consistent performance. The dual dipole feed of the present invention utilizes a pair of stacked dipoles etched onto a printed circuit board which directly couples with a coaxial cable. The stacked dipole design exhibits a narrowed lobe which provides greater directivity and, therefore, greater gain. In addition, the stacked dipole antenna minimizes cross polarization with minimal operating side lobes. Finally, the present invention integrates a phasing power combiner and a matching network to an unbalanced coaxial cable. A sub-reflector is also used to enhance the performance of the stacked dual dipole feed.